JP5287593B2 - Manufacturing method of positive electrode active material. - Google Patents

Description

The present invention relates to a method for producing a lithium reversibly doped / dedoped positive electrode active substance.

  In recent years, along with dramatic progress of various electronic devices, research on rechargeable secondary batteries as batteries that can be used conveniently and economically for a long time has been conducted. As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium secondary batteries and the like are known.

  Among the secondary batteries as described above, the lithium secondary battery has advantages such as high output and high energy density. A lithium secondary battery is composed of a positive electrode and a negative electrode having an active material capable of reversibly removing and inserting lithium ions, and a non-aqueous electrolyte.

As the positive electrode active material of the lithium secondary battery, metal oxide, metal sulfide, polymer, or the like is used. For example, a lithium-free compound such as TiS ₂ , MoS ₂ , NbSe ₂ , V ₂ O ₅ , LiMO ₂ (M = Co, Ni, Mn, Fe, etc.), lithium composite oxides such as LiMn ₂ O ₄ are known.

Currently, LiCoO ₂ is widely put into practical use as a positive electrode active material having a potential of 4 V with respect to lithium. This LiCoO ₂ has a high energy density and a high voltage, and is an ideal positive electrode material in various aspects.

  However, since Co is unevenly distributed on the earth and is a scarce resource, there are problems that it is expensive and stable supply is difficult. Therefore, it is desired to develop positive electrode materials based on inexpensive Ni and Mn, which are abundant as resources instead of Co.

The positive electrode containing LiNiO ₂ has a large theoretical capacity and a high discharge potential, but the crystal structure of LiNiO ₂ collapses as the charge / discharge cycle progresses. For this reason, there exist problems, such as causing the fall of discharge capacity and being inferior to thermal stability.

As a positive electrode material based on Mn, LiMn ₂ O ₄ having a positive spinel structure and having a space group Fd3m has been proposed. This LiMn ₂ O ₄ has a high potential equivalent to LiCoO ₂ , ie, a 4V class with respect to the lithium potential. Furthermore, LiMn ₂ O ₄ is a very promising material because it is easy to synthesize and has a high battery capacity, and has been put to practical use.

However, in the case of a battery actually configured using LiMn ₂ O ₄ , there is a problem that the capacity and the cycle characteristics are not sufficient, such as large capacity deterioration during high-temperature storage and Mn dissolving in the electrolyte. Is left.

Therefore, Patent Document 1 proposes that a phosphate compound of transition metal M having an olivine structure (M is Fe, Mn, Co, Ni) is used for a positive electrode of a lithium ion battery. Further, Patent Document 2 proposes using, for example, LiFePO ₄ as a positive electrode of a lithium ion battery among the above-described phosphate compounds of transition metal M having an olivine structure.

LiFePO ₄ has a large volume density of 3.6 g / cm ³ , generates a high potential of 3.4 V, and has a large theoretical capacity of 170 mAh / g. Moreover, LiFePO ₄ is a promising material as a positive electrode active material of a lithium ion battery because it contains one electrochemically dedopeable Li per Fe atom in the initial state.

However, as reported in the above publication, an actual battery constructed using LiFePO ₄ as the positive electrode active material has only obtained an actual capacity of about 60 mAh / g to 70 mAh / g. Thereafter, a non-patent document 1 reports an actual capacity of about 120 mAh / g. However, considering that the theoretical capacity is 170 mAh / g, it cannot be said that the capacity is sufficient. Moreover, the discharge voltage of LiFePO ₄ is 3.4 V, and there is a problem that the discharge voltage is lower than that of the positive electrode material used in current lithium ion batteries.

Therefore, it has been proposed to use LiMnPO ₄ for the positive electrode of a lithium ion battery as a phosphoric acid compound having an olivine structure mainly composed of Mn, which is an element having a higher redox potential than Fe.

JP-A-9-134724

Japanese Patent Laid-Open No. 9-171827

Journal of the Electrochemical Society, 144,1188 (1997)

However, conventional phosphoric acid compounds having a basic composition of LiMnPO ₄ and having an olivine structure mainly composed of Mn are difficult to generate redox of Mn. According to Non-Patent Document 1 , an example of Mn-based olivine structure having an olivine structure capable of Mn redox generation is LiMn _x Fe ₁ having a structure in which a part of Mn is substituted with Fe. _-x Reported as PO ₄ only.

Further, according to Non-Patent Document 1 , an actual battery configured using LiMn _x Fe _1-x PO ₄ as a positive electrode active material has been reported to have an actual capacity of about 80 mAh / g. Is 170 mAh / g, it cannot be said that it has a sufficient capacity.

Further, according to Non-Patent Document 1 , in an actual battery configured using LiMn _x Fe _1-x PO ₄ as a positive electrode active material, when the composition y of Mn exceeds 0.5, the capacity decreases. It has been reported to cause. That is, according to the above paper, when the composition of Mn in LiMn _x Fe _1-x PO ₄ is increased, a high voltage can be obtained, but the capacity is lowered, which is inconvenient as a practical material. . On the other hand, if the composition of Mn in LiMn _x Fe _1-x PO ₄ is kept low in order to obtain a high capacity, the composition of Mn as the main component of redox will be low and the redox potential will be high. There is a problem that the excellent characteristics of Mn cannot be obtained sufficiently. Furthermore, when the discharge voltage is lowered, there is a disadvantage that compatibility with the current lithium ion battery is lost.

Thus, it has been extremely difficult for LiMn _x Fe _1-x PO ₄ to achieve both high capacity and high discharge voltage.

The present invention has been proposed in view of such conventional circumstances, without reducing the capacity to achieve a high discharge voltage, provides a method for producing a positive electrode active substance which exhibits excellent charging and discharging characteristics The purpose is to do.

In order to achieve the above-described object, a method for producing a positive electrode active material according to the present invention includes:
Formula _{Li x Mn y Fe 1-y} PO 4 ( where 0 <x ≦ 2, 0.5 <y <0.95.) The method of producing a cathode active material containing a compound represented by Because
A mixing step of mixing a plurality of substances as raw materials for compound synthesis into a precursor;
A firing step of firing and reacting the precursor obtained in the mixing step,
The plurality of substances includes iron oxalate,
The firing temperature of the precursor in the firing step is in the range of 350 ° C. or more and 790 ° C. or less,
In the mixing step, a reducing agent is added and mixed to form a precursor,
The reducing agent is iron powder ,
The iron powder is characterized by being added to the precursor in the range of 1 to 30% by weight with respect to the total amount of Fe in the iron raw material among the synthetic raw materials .

The manufactured positive electrode active material as described _{above, Li x Mn y Fe 1-} y PO 4 is formed by replacing a part of Mn by Fe. This Fe is yarn due to Mn ³⁺ - it is possible to dilute the Teller effect, it is possible to suppress the distortion of the crystal structure of _{Li x Mn y Fe 1-y} PO 4. Further, since the composition y of Mn is in the range of 0.5 <y <0.95, a high discharge voltage can be realized without reducing the capacity.

As apparent from the above description, according to the present _{invention, Li x Mn y Fe 1-} y PO 4 to be used as the positive electrode active material is formed by replacing a part of Mn by Fe. This Fe is yarn due to Mn ³⁺ - it is possible to dilute the Teller effect, it is possible to suppress the distortion of the crystal structure of _{Li x Mn y Fe 1-y} PO 4. Further, since the composition y of Mn is in the range of 0.5 <y <0.95, a high discharge voltage region in the vicinity of 4 V can be expanded without reducing the capacity. Therefore, redox generation of Mn is possible, and a positive electrode active material that realizes a high capacity and a high discharge voltage can be provided.

Further, as is clear from the above description, according to the present invention, the nonaqueous electrolyte battery can generate Mn redox as a positive electrode active material, and achieve a high capacity and a high discharge voltage. It is used _{x Mn y Fe 1-y PO} 4. Therefore, it is possible to provide a nonaqueous electrolyte battery that has excellent charge / discharge characteristics and can be compatible with current lithium batteries.

It is sectional drawing which shows one structural example of the nonaqueous electrolyte battery concerning this invention. In Example 1, 450 ° C., of 500 ° C., heated at 600 ° C. or 700 ° C., synthesized LiMn _0.6 Fe _0.4 PO _4, is a diagram showing the respective powder X-ray diffraction pattern. FIG. 3 is a diagram showing a powder X-ray diffraction pattern of LiMnPO ₄ synthesized in Comparative Example 1. The LiMn _0.6 Fe _0.4 PO _4, synthesized at 600 ° C. In Example 1, a diagram showing charge-discharge characteristics of the battery using as the positive electrode active material. The LiMnPO ₄ synthesized in Comparative Example 1 is a diagram showing charge-discharge characteristics of the battery using as the positive electrode active material. FIG. ₄ is a diagram showing powder X-ray diffraction patterns of LiMn _0.7 Fe _0.3 PO ₄ synthesized in Example 2 and LiMn _0.75 Fe _0.25 PO ₄ synthesized in Example 3. The LiMn _0.7 Fe _0.3 PO _4, synthesized in Example 2 is a diagram showing the charge and discharge characteristics of the battery using as the positive electrode active material. The LiMn _0.75 Fe _0.25 PO ₄ synthesized in Example 3, is a diagram showing charge-discharge characteristics of the battery using as the positive electrode active material. The LiMn _0.7 Fe _0.3 PO _4, synthesized in Example 2 is a diagram showing the cycle characteristics of the battery using as the positive electrode active material. 6 is a diagram showing a powder X-ray diffraction pattern of LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ synthesized in Example 4. FIG. The LiMn0 _.7 Fe _0.2 Ti _0.1 PO _4, synthesized in Example 4 is a diagram showing charge-discharge characteristics of the battery using as the positive electrode active material. 6 is a diagram showing a powder X-ray diffraction pattern of LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ synthesized in Example 5. FIG. The LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ synthesized in Example 5, is a diagram showing charge-discharge characteristics of the battery using as the positive electrode active material.

  Hereinafter, specific embodiments of a positive electrode active material and a nonaqueous electrolyte battery according to the present invention will be described in detail with reference to the drawings.

In the present invention, the positive electrode active material has an olivine structure represented by the general formula _{Li x Mn y Fe 1-y} PO 4 ( proviso that 0 <x ≦ 2, is 0.5 <y <0.95. ) Is contained.

Conventionally, LiMnPO ₄ which is a compound having an olivine structure mainly composed of Mn has been difficult to operate as a battery when used as a positive electrode active material of a lithium secondary battery. The reason for this is not necessarily clear, but it is presumed that this is because of the following reasons.

When the battery is charged, that is, as Li is extracted from LiMnPO ₄ having an olivine structure, Mn ²⁺ is oxidized to Mn ³⁺ . Mn ³⁺ causes a yarn-teller effect and causes interaction between elements of Mn ³⁺ —O—Mn ³⁺ . The interaction between elements due to the yarn-teller effect distorts the entire crystal structure of LiMnPO ₄ , making Mn redox difficult and impeding operation as a battery.

Therefore, the positive electrode active material according to the present invention, in LiMnPO ₄ having an olivine structure mainly composed of Mn, and containing the structural _{Li x Mn y Fe 1-y} PO 4 of formed by replacing a part of Mn by Fe ing.

Then, Fe are partially substituted Mn occurs when the _{Li x Mn y Fe 1-y} PO 4 is a charging state, the interaction between the elements of Mn ³⁺ -O-Mn ³⁺ Can be cut. That is, the yarn according to Mn ³⁺ - for Teller effect is diluted, the strain of the entire crystal structure of _{Li x Mn y Fe 1-y} PO 4 is suppressed to a level capable of realizing the redox generation of Mn. Thus, positive electrode active material containing a compound represented by _{Li x Mn y Fe 1-y} PO 4 has the olivine structure, realizes redox generation of Mn, it is possible to operate as a battery.

Incidentally, the charge-discharge characteristics of the _{Li x Mn y Fe 1-y} PO 4 , first to the 4V around and then 3.6V around, shows two characteristic flat discharge voltage region. In the conventional _{Li x Mn y Fe 1-y} PO 4, increasing the ratio of Mn to the high voltage, that is, the composition y of Mn exceeds 0.5, the discharge capacity of the entire battery is reduced It was. For this reason, the excellent characteristic of Mn having a high oxidation-reduction potential could not be sufficiently exhibited, and only a low discharge voltage was obtained.

_{However, Li x Mn y Fe 1-} y PO 4 synthesized by techniques such as described below, the composition y of Mn is possible to maintain the high discharge capacity even in a range exceeding 0.5 . Accordingly, the _{Li x Mn y Fe 1-y} PO 4, the proportion of Mn is high oxidation-reduction potential elements, it is possible to increase relative to the Fe, 4V vicinity of a higher voltage The capacity of the discharge voltage can be improved. _{That, Li x Mn y Fe 1-} y PO 4 , when the composition y of Mn exceeds 0.5, while maintaining a high capacity, it is possible to realize a high discharge voltage.

Specifically, the composition y of Mn is in the range of 0.5 <y <0.95. That is, when the composition y of Mn is 0.5 or less, because the proportion of Mn occupying the _{Li x Mn y Fe 1-y} PO 4 is small, thereby causing a decrease in discharge voltage. On the other hand, when the composition y of Mn is 0.95 or more, since the proportion of Fe is too small, there is a possibility that the effect of diluting the yarn-teller effect by Fe may be insufficient, and Mn redox generation is difficult. Become.

_{Moreover, Li x Mn y Fe 1-} y PO 4 , it is preferable to include those having a particle diameter of at 10μm or less. As _{Li x Mn y Fe 1-y} PO 4 where the positive electrode active material contains, if not include any particle size is 10μm or less, mostly those crystallization becomes excessively advanced giant particles May occupy. For this reason, there is a possibility that lithium as a charge carrier cannot be smoothly diffused in the particles of the positive electrode active material.

  By including the particles having a particle diameter of 10 μm or less, the diffusion of lithium ions in the positive electrode active material can be made smooth.

Further, this _{Li x Mn y Fe 1-y} PO 4 is preferably Brunauer-Emmet Taylor (BET) specific surface area of 0.5 m ² / g or more. In the case of a positive electrode active material having a large particle size, the surface area becomes small. When a large current is passed under such circumstances, that is, when a large amount of lithium ions is introduced into the active material in a short time, the diffusion of lithium in the active material cannot catch up with the supply of lithium from the outside, and the apparent capacity is increased. Decrease. Therefore, in order to secure a sufficient capacity even under a large current, a technical measure is required to increase the specific surface area and, as described above, to reduce the particle size.

The BET specific surface area of the _{Li x Mn y Fe 1-y} PO 4 With 0.5 m ² / g or more, it was quickly diffusion of lithium in the active material, to secure a sufficient capacity even under a large current Can do.

Incidentally, the compound represented by the general formula _{Li x Mn y Fe 1-y} PO 4 described above, a part of Mn, in combination with Fe, and at least one metal element A selected from Ti or Mg substituted It does not matter even if it is a structure. That is, the positive electrode active material is represented by the general formula _{Li x Mn y Fe z A 1-} (y + z) PO 4 ( proviso that 0 <x ≦ 2, a 0.5 <y <0.95, 0. 5 <y + z <1, and A is at least one metal element selected from Ti and Mg).

In this _{Li x Mn y Fe z A 1-} (y + z) PO 4, substitution element A is similar to the above _{Fe, Li x Mn y Fe z} A 1- (y + z) PO 4 is charged state The interaction between the elements of Mn ³⁺ —O—Mn ³⁺ that occurs when That is, the yarn according to Mn ³⁺ - for Teller effect is _{diluted, Li x Mn y Fe z A} 1- (y + z) strain as a whole the crystal structure of PO ₄ is redox generate feasible levels of Mn To be suppressed. Thus, positive electrode active material containing a compound represented by _{Li x Mn y Fe z A 1-} (y + z) PO 4 has the olivine structure, to achieve redox generation of Mn, operates as a battery Is possible.

Then, as described above, for the synthesis method of a phosphate compound having an olivine structure mainly composed of Mn, the general formula _{Li x Mn y Fe 1-y} PO compounds represented by ₄ will be described as an example.

To synthesize _{Li x Mn y Fe 1-y} PO 4 , first, the general formula _{Li x Mn y Fe 1-y} PO 4 by mixing multiple substances to be raw material for synthesizing the compound represented by the by the precursor A mixing step is performed. Next, a firing step is performed in which the precursor obtained in the mixing step is fired and reacted.

In the mixing step, iron oxalate as a raw material, (FeC ₂ O ₄ ), manganese carbonate (MnCO ₃ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) Are mixed in a predetermined ratio to obtain a precursor.

In the mixing step, the synthesis raw materials are sufficiently mixed. Synthetic raw material by mixing thoroughly, the raw material mixes in uniform, the contact point is increased, it is possible to synthesize _{Li x Mn y Fe 1-y} PO 4 at a lower than conventional temperature.

In the firing step, the precursor is heated at a predetermined temperature in an inert gas atmosphere such as nitrogen. _{Thus, Li x Mn y Fe 1-} y PO 4 is synthesized.

Iron oxalate used as a synthetic raw material has a lower decomposition temperature than iron phosphate or the like conventionally used as a synthetic raw material. Therefore, by using the iron oxalate as the starting materials for synthesis can proceed rapidly the synthesis of _{Li x Mn y Fe 1-y} PO 4. Further, by using the iron oxalate as a starting material for the synthesis of _{Li x Mn y Fe 1-y} PO 4, at the time of firing, acid gases, etc., since the gas that affects around does not occur, damaging the reactor, etc. There is no.

In the synthesis method as described above, by using iron oxalate as a synthesis raw material and firing the precursor in a nitrogen stream, Li _x Mn at a temperature much lower than the conventional 800 ° C., for example, 300 ° C. _y Fe _1-y PO ₄ can be synthesized. In other words, it is possible to synthesize _{Li x Mn y Fe 1-y} PO 4 in a wider temperature range as compared with the conventional art will, temperature of firing the precursor (hereinafter, referred to as the firing temperature.) Width of the selection of Spread. When the calcination temperature is as high as 800 ° C. as in the prior art, energy is consumed correspondingly, and the load applied to the reaction apparatus and the like is large.

The present _{inventors, Li x Mn y Fe 1-} y and the temperature of firing the precursor PO ₄ in the synthesis of the capacity of the battery using the _{Li x Mn y Fe 1-y} PO 4 as an active material focusing on the relationship was studied optimum sintering temperature for synthesizing _{Li x Mn y Fe 1-y} PO 4 to realize a high capacity.

As a result, Li _x Mn _y Fe firing temperature of firing the precursor of _1-y PO ₄ is 350 ° C. or higher, it was found that it is preferable to set a temperature in the range of 790 ° C. or less. If the firing temperature is lower than 350 ° C., the chemical reaction and crystallization there is a possibility that not proceed sufficiently, it may be impossible to obtain a uniform _{Li x Mn y Fe 1-y} PO 4. Further, if the firing temperature is higher than 790 ° C., crystallization may proceed excessively and lithium diffusion may be hindered. Therefore, 350 ° C. or higher, by firing the precursor in the range of 790 ° C. or less to synthesize the _{Li x Mn y Fe 1-y} PO 4 , to obtain a uniform _{Li x Mn y Fe 1-y} PO 4 can, it is possible to realize a high capacity over conventional Li _x was synthesized by the production method Mn _y Fe _1-y PO is a volume of ₄ 120 mAh / g.

The firing temperature is more preferably in the range of 450 ° C. or higher and 700 ° C. or lower. 450 ° C. or higher, by firing the precursor in less than 700 ℃ to synthesize the _{Li x Mn y Fe 1-y} PO 4, Li x Mn y Fe 1-y PO is a theoretical capacity of ₄ 170 mAh / g High real capacity approaching can be obtained.

In the method of manufacturing the positive electrode active material as described above in the synthesis of _{Li x Mn y Fe 1-y} PO 4, because of the use of iron oxalate as starting materials for synthesis, in addition to the synthesis reaction proceeds rapidly, the reaction No gas is generated that affects the surroundings. Thus, it is possible than conventional at a low temperature to obtain a _{Li x Mn y Fe 1-y} PO 4 of the single-phase. Therefore, according to the method of manufacturing the positive electrode active material, it is possible to obtain the _{Li x Mn y Fe 1-y} PO 4 to realize a high capacity.

Incidentally, in the synthesis of _{Li x Mn y Fe 1-y} PO 4, the air in the precursor is left, Fe ²⁺ of oxalate in iron is a bivalent iron compound, in the air Oxidized by oxygen to Fe ³⁺ . Therefore, the iron compound trivalent are impurities, can be introduced during _{Li x Mn y Fe 1-y} PO 4 , synthesized.

For this reason, in the mixing step, iron oxalate as a raw material, (FeC ₂ O ₄ ), manganese carbonate (MnCO ₃ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li It is preferable to add, for example, iron powder (Fe) as a reducing agent to a mixture of ₂ CO ₃ ) at a predetermined ratio, and sufficiently mix these substances into a precursor.

The iron powder contained in the precursor is obtained when Fe ^{2+ in} iron oxalate, which is a divalent iron compound, is oxidized by oxygen in the air contained in the precursor to become Fe ^3+. Reduce Fe ³⁺ to Fe ²⁺ . This makes it possible to trivalent iron compound not mixed in the _{Li x Mn y Fe 1-y} PO 4 , synthesized to obtain a _{Li x Mn y Fe 1-y} PO 4 of the single-phase.

Moreover, this iron powder, with is added as a reducing agent, becomes a part of the starting materials for synthesis, is synthesized in the _{Li x Mn y Fe 1-y} PO 4 as the final product. Thus, to obtain the reducing agent is part of a synthetic raw material of _{Li x Mn y Fe 1-y} PO 4 , there is no fear that impurities are mixed, the _{Li x Mn y Fe 1-y} PO 4 of the single-phase Can do. Also, when a reducing agent as a part of the starting materials for synthesis _{Li x Mn y Fe 1-y} PO 4, it is not necessary to remove the reducing agent which remains after completion of the _{reaction, Li x Mn y Fe 1-} y PO 4 Can be efficiently synthesized.

When using iron powder as part of the starting materials for synthesis of a reducing agent or _{Li x Mn y Fe 1-y} PO 4, the iron powder is in the range of 1% to 30% by weight relative to the sum of Fe in the iron starting material And is preferably added to the precursor. If the amount of iron powder added is less than 1% by weight, the oxidation of Fe ²⁺ may not be sufficiently prevented. Further, since iron powder (Fe) is less reactive than Fe ²⁺ in iron oxalate (FeC ₂ O ₄ ), if the amount of iron powder added is more than 30% by weight, Li _x Mn _y There is a possibility that the synthesis reaction of Fe _1-y PO ₄ does not proceed sufficiently.

Therefore, the amount of iron powder added is in the range of 1 to 30% by weight with respect to Fe in the iron raw material, so that the oxidation of Fe ²⁺ is prevented without interfering with the synthesis reaction. of _{Li x Mn y Fe 1-y} PO 4 can be obtained.

  As the reducing agent, oxalic acid, formic acid, hydrogen, and the like can be used as the reducing agent in addition to the iron powder as long as no solid product remains after the firing step.

In the method of manufacturing the positive electrode active material as described above, since the addition of the reducing agent in the precursor in synthesizing _{Li x Mn y Fe 1-y} PO 4, are anti-oxidation of Fe ²⁺ is, impurities it can be mixed in without, to synthesize _{Li x Mn y Fe 1-y} PO 4 of the single-phase. Further, it is possible to synthesize _{Li x Mn y Fe 1-y} PO 4 at a lower temperature than conventional. Therefore, according to the positive electrode active material, it is possible to obtain the _{Li x Mn y Fe 1-y} PO 4 to realize a high capacity.

By using the _{Li x Mn y Fe 1-y} PO 4 , synthesized as described above in the positive electrode active material, lithium ion doping / undoping is performed satisfactorily, has a high capacity, cycle A nonaqueous electrolyte battery having excellent characteristics can be manufactured.

_{Moreover, Li x Mn y Fe 1-} y PO 4 as the positive electrode active material, it can also be prepared as shown below. First, a general formula _{Li x Mn y Fe 1-y} PO 4 in a mixture of a plurality of materials as a raw material for synthesizing the compound represented by the precursor mixing step. Next, the deaeration process which removes the air contained in the precursor obtained at the mixing process is performed. By performing the sintering step and reacted with firing the precursor air is removed in the degassing step, obtaining a _{Li x Mn y Fe 1-y} PO 4.

In the mixing step, iron acetate (Fe (CH ₃ COO) ₂ ), manganese carbonate (MnCO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO) that are synthetic raw materials are used. ₃ ) is mixed at a predetermined ratio to obtain a precursor.

  In the degassing step, the precursor is sufficiently homogenized and subjected to a deaeration process to remove air contained in the precursor. As the deairing treatment, for example, an inert gas is introduced after the atmosphere of the precursor is replaced with vacuum. Thereby, the air contained in a precursor is removed. As another example of the deairing treatment, for example, a solvent having a boiling point of 250 ° C. or less is allowed to coexist with the precursor, and the solvent is evaporated in an inert gas. Thereby, the air contained in a precursor is removed. Examples of the solvent having a boiling point of 250 ° C. or lower include water and ethanol.

In the firing step, the precursor that has been deaired is fired at a predetermined temperature in an inert gas atmosphere such as nitrogen. _{Thus, Li x Mn y Fe 1-} y PO 4 is synthesized.

During the synthesis of the _{Li x Mn y Fe 1-y} PO 4, the air in the precursor is left, Fe ²⁺ of acetate in the iron is bivalent iron compound, is oxidized by oxygen in the air And may be Fe ³⁺ . Therefore, trivalent iron compounds, may be mixed as an impurity in the _{Li x Mn y Fe 1-y} PO 4 , synthesized.

For this reason, in the said deaeration process, the deaeration process is performed, the air contained in a precursor is removed, and the oxidation of Fe ^<2+> in iron acetate is prevented. This makes it possible to trivalent iron compound not mixed in the _{Li x Mn y Fe 1-y} PO 4 , synthesized to obtain a _{Li x Mn y Fe 1-y} PO 4 of the single-phase.

The firing temperature is a temperature of firing the precursor in synthesizing the _{Li x Mn y Fe 1-y} PO 4 , as well as the range of firing temperature as described above, 350 ° C. or higher, and the range of 790 ° C. or less It is preferable to do.

In the method of manufacturing the positive electrode active material as described above in the synthesis of _{Li x Mn y Fe 1-y} PO 4, since the removal of air contained in the precursor, the oxidation of Fe ²⁺ is prevented . Thereby, impurities are not _{mixed, Li x Mn y Fe 1-} y PO 4 of the single phase is obtained. Further, it is possible to synthesize _{Li x Mn y Fe 1-y} PO 4 at a low firing temperature. Therefore, according to the method of manufacturing the positive electrode active material, it is possible to obtain the _{Li x Mn y Fe 1-y} PO 4 to realize a high capacity.

By using the _{Li x Mn y Fe 1-y} PO 4 , synthesized as described above in the positive electrode active material, lithium ion doping / undoping is performed satisfactorily, has a high capacity, cycle A nonaqueous electrolyte battery having excellent characteristics can be manufactured.

_{Moreover, Li x Mn y Fe 1-} y PO 4 to be used as the positive electrode active material, it can also be prepared as shown below. In this case, the positive electrode active material containing _{Li x Mn y Fe 1-y} PO 4 is synthesized as a composite sample consisting of _{Li x Mn y Fe 1-y} PO 4 and the conductive material.

First, the mixing step of the _{Li x Mn y Fe 1-y} PO 4 several substances were mixed with the precursor to be the raw material for synthesizing. Next, a firing step is performed in which the precursor obtained in the mixing step is fired and reacted. At this time, a conductive material is added to the synthetic raw material or precursor.

  Examples of the conductive material include carbon, silver, and a conductive polymer. Examples of carbon include various carbon blacks such as graphite and acetylene black.

The conductive material is, relative to 100 parts by weight of _{Li x Mn y Fe 1-y} PO 4, it is preferably added in the range of 0.5 to 20 parts by weight. When the amount of the conductive material is less than 0.5% by weight, a sufficient effect may not be obtained. On the other hand, if the amount of conductive material exceeds 20 _{wt%, Li x Mn y Fe 1} -y PO 4 as the main component of the oxide is less percentage of the positive electrode active material, the energy density of the nonaqueous electrolyte battery May be smaller.

Thus, positive electrode active material, conductive material relative to 100 parts by weight of _{Li x Mn y Fe 1-y} PO 4, by being added in an amount of 0.5 to 20 parts by weight, load characteristics and electrode A non-aqueous electrolyte battery that achieves improved formability and uses the composite sample as a positive electrode active material has a high capacity.

Manufacturing method for synthesizing the composite sample as the positive electrode active material, wherein the _{Li x Mn y Fe 1-y} PO 4 is a _{Li x Mn y Fe 1-y} PO 4 carbon composite comprising a carbon as a conductive material A manufacturing method to be synthesized will be described.

Li _x Mn _y Fe _1-y when adding carbon to the precursor of PO _4, in the mixing step, as a synthetic raw material, iron oxalate (FeC ₂ O _4), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), Lithium carbonate (Li ₂ CO ₃ ), manganese acetate tetrahydrate (Mn (CH ₃ OO) ₂ .4H ₂ O) or manganese carbonate (MnCO ₃ ) in a predetermined ratio and mixed thoroughly to give a precursor. Let it be the body. Next, the precursor is calcined at a low temperature in an inert gas atmosphere such as nitrogen. Then, the calcined precursor and carbon are mixed and pulverized. In the baking step, and fired at a predetermined temperature in an inert gas atmosphere such as nitrogen, thereby obtaining a _{Li x Mn y Fe 1-y} PO 4 carbon composite.

Moreover, Li _x Mn _y if Fe adding carbon to the synthesis of the raw material of _1-y PO _4, in the mixing step, the iron oxalate (FeC ₂ O _4), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), Lithium carbonate (Li ₂ CO ₃ ) and manganese acetate tetrahydrate (Mn (CH ₃ OO) ₂ .4H ₂ O) or manganese carbonate (MnCO ₃ ) And then calcined at a low temperature in an inert gas atmosphere such as nitrogen. In the baking step, and further calcinated at a predetermined temperature in an inert gas atmosphere such as nitrogen, thereby obtaining a _{Li x Mn y Fe 1-y} PO 4 carbon composite.

In the synthesis method as described above, the precursor is prepared by sufficiently mixing the synthesis raw materials. By sufficiently mixing the synthetic raw materials, it is possible to obtain a precursor in which the respective raw materials are uniformly mixed and contact points are increased. Then, this by a precursor to performing firing the synthesis in a nitrogen stream, for example, as 300 ° C., as compared with the conventional method in _{Li x Mn y Fe 1-y} PO 4 is a sintering temperature for synthesizing 800 ° C. It became possible to synthesize precursor samples by firing the precursor at a much lower temperature.

In other words, it is possible to synthesize _{Li x Mn y Fe 1-y} PO 4 carbon composite in a wide temperature range, the range of selection of the temperature at the time of synthesis is widened. The firing temperature is preferably 350 ° C. or higher and 790 ° C. or lower, and more preferably 450 ° C. or higher and 700 ° C. or lower.

As described above, Li _x Mn In _y Fe _1-y PO ₄ and the conductive material and the method for producing a cathode active material for synthesizing a complex sample consisting _{of, Li x Mn y Fe 1-} y PO 4 consisting solely positive Compared with the active material, it is possible to synthesize a positive electrode active material exhibiting good load characteristics and electrode formability. In addition, the positive electrode active material manufactured in this way can achieve good load characteristics and electrode formability even when a small amount of a conductive agent is added at the time of electrode preparation, and has a large volume density. A conductive agent such as graphite can be used.

  Therefore, the non-aqueous electrolyte battery containing this composite sample as the positive electrode active material has a high capacity and good cycle characteristics because electrons move smoothly in the electrode. Moreover, since it is not necessary to add a new conductive agent to the positive electrode mixture as a nonaqueous electrolyte battery, the electrode volume can be maintained high, and the energy density is high.

In the above description, the general formula Li _x Mn _y Fe method for the synthesis of _1-y PO compounds represented by ₄ has been described as an example, the general formula _{Li x Mn y Fe z A 1-} (y + in case of synthesizing _z) represented by PO ₄ compounds, similar to the method by mixing a substance which is a synthetic raw material of the metal element a, except that the synthesis of the _{Li x Mn y Fe 1-y} PO 4 described above by _{the, Li x Mn y Fe z a} 1- (y + z) PO 4 is obtained.

  Next, the structure of the nonaqueous electrolyte battery using the positive electrode active material as described above will be described with reference to FIG.

  As shown in FIG. 1, the nonaqueous electrolyte battery 1 includes a negative electrode 2, a negative electrode can 3 that contains the negative electrode 2, a positive electrode 4, a positive electrode can 5 that contains the positive electrode 4, and a positive electrode 4 and a negative electrode 2. The separator 6 and the insulating gasket 7 are provided between them, and the negative electrode can 3 and the positive electrode can 5 are filled with a non-aqueous electrolyte.

  The negative electrode 2 is formed by forming a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector. As the negative electrode current collector, for example, nickel foil, copper foil or the like is used.

  As the negative electrode active material, a material that can be doped / undoped with lithium is used. Specifically, lithium metal, lithium alloy, conductive polymer doped with lithium, layered compound (carbon material, metal oxide, etc.) Etc. are used.

  As a binder contained in a negative electrode active material layer, the well-known resin material etc. which are normally used as a binder of the negative electrode active material layer of this kind of nonaqueous electrolyte battery can be used.

  Moreover, as a negative electrode, you may use the metal lithium foil used as a negative electrode active material, for example.

  The negative electrode can 3 accommodates the negative electrode 2 and serves as an external negative electrode of the nonaqueous electrolyte battery 1.

The positive electrode 4 is formed by forming a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector. In the nonaqueous electrolyte battery 1, as a positive electrode active material contains a compound represented by _{Li x Mn y Fe 1-y} PO 4 or _{Li x Mn y Fe z A 1-} (y + z) PO 4 as described above ing. For example, an aluminum foil or the like is used as the positive electrode current collector.

  As a binder contained in a positive electrode active material layer, the well-known resin material etc. which are normally used as a binder of the positive electrode active material layer of this kind of nonaqueous electrolyte battery can be used.

  The positive electrode can 5 accommodates the positive electrode 4 and serves as an external positive electrode of the nonaqueous electrolyte battery 1.

  The separator 6 separates the positive electrode 4 and the negative electrode 2, and a known material that is usually used as a separator for this type of nonaqueous electrolyte battery can be used. For example, a polymer film such as polypropylene is used. Used. Moreover, the thickness of a separator needs to be as thin as possible from the relationship between lithium ion conductivity and energy density. Specifically, the thickness of the separator is preferably 50 μm or less, for example.

  The insulating gasket 7 is incorporated in and integrated with the negative electrode can 3. The insulating gasket 7 is for preventing leakage of the non-aqueous electrolyte filled in the negative electrode can 3 and the positive electrode can 5.

  As the non-aqueous electrolyte, a solution in which an electrolyte is dissolved in an aprotic non-aqueous solvent is used.

  Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyllactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, 3-methyl1 , 3-dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and the like can be used. In particular, from the viewpoint of voltage stability, it is preferable to use cyclic carbonates such as propylene carbonate and vinylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and dipropyl carbonate. Moreover, such a non-aqueous solvent may be used individually by 1 type, and may be used in mixture of 2 or more types.

As the electrolyte dissolved in the non-aqueous solvent, for example, lithium salts such as LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used. Among these lithium salts, it is preferable to use LiPF ₆ or LiBF ₄ .

As described above, the nonaqueous electrolyte battery 1, as a cathode active _{material, Li x Mn y Fe 1-} y PO 4 or _{Li x Mn y Fe z A 1-} (y + z) a compound represented by PO ₄ Contains. These _{Li x Mn y Fe 1-y} PO 4 and _{Li x Mn y Fe z A 1-} (y + z) PO 4 is a composition y of Mn, is in the range of 0.5 <y <0.95 Therefore, a high discharge voltage is realized without reducing the discharge capacity. _{Therefore, Li x Mn y Fe 1-} y PO 4 or _{Li x Mn y Fe z A 1-} (y + z) a non-aqueous electrolyte battery 1 using a PO ₄ as the positive electrode active material, realize a high discharge voltage in the vicinity 4V In addition, it has excellent charge / discharge characteristics. Furthermore, since the capacity in the high voltage region near 4 V is improved, compatibility with current lithium batteries can be achieved.

_{Then, Li x Mn y Fe 1-} y PO 4 or _{Li x Mn y Fe z A 1-} (y + z) a non-aqueous electrolyte cell 1 employing the PO ₄ as the positive electrode active material, for example, as follows manufacturing Is done.

  As the negative electrode 2, first, a negative electrode active material and a binder are dispersed in a solvent to prepare a slurry negative electrode mixture. Next, the negative electrode 2 is produced by uniformly coating the obtained negative electrode mixture on a current collector and drying to form a negative electrode active material layer. As the binder of the negative electrode mixture, a known binder can be used, and a known additive or the like can be added to the negative electrode mixture. Moreover, the metallic lithium used as a negative electrode active material can also be used as the negative electrode 2 as it is.

As the positive electrode 4, first, a _{Li x Mn y Fe 1-y} PO 4 or _{Li x Mn y Fe z A 1-} (y + z) PO 4 and the electrically conductive agent and a binder such as graphite as a positive electrode active material Is dispersed in a solvent to prepare a slurry positive electrode mixture. Next, the positive electrode 4 is produced by uniformly coating the obtained positive electrode mixture on a current collector and drying to form a positive electrode active material layer. As the binder of the positive electrode mixture, a known binder can be used, and a known additive or the like can be added to the positive electrode mixture.

  The nonaqueous electrolytic solution is prepared by dissolving an electrolyte salt in a nonaqueous solvent.

  Then, the negative electrode 2 is accommodated in the negative electrode can 3, the positive electrode 4 is accommodated in the positive electrode can 5, and a separator 6 made of a polypropylene porous film or the like is disposed between the negative electrode 2 and the positive electrode 4. The nonaqueous electrolyte battery 1 is completed by injecting a nonaqueous electrolyte into the negative electrode can 3 and the positive electrode can 5 and caulking and fixing the negative electrode can 3 and the positive electrode can 5 via the insulating gasket 7.

As described above, the positive electrode active material, the general formula _{Li x Mn y Fe 1-y} PO 4 ( proviso that 0 <x ≦ 2, is 0.5 <y <0.95.) Represented by compound, or the general formula _{Li x Mn y Fe z a 1-} (y + z) PO 4 ( where 0 <x ≦ 2, a 0.5 <y <0.95, 0.5 < y + z < 1 and A is at least one metal element selected from Ti and Mg). Thus, the positive electrode active material occurs when the _{Li x Mn y Fe 1-y} PO 4 or _{Li x Mn y Fe z A 1-} (y + z) PO 4 is a charging state, the Mn ³⁺ The resulting yarn-teller effect is diluted. Thus, is _{Li x Mn y Fe 1-y} PO 4 or _{Li x Mn y Fe z A 1-} (y + z) strain of the crystal structure of PO ₄ is suppressed, having an olivine structure mainly composed of conventional Mn Mn redox generation, which was difficult as a phosphoric acid compound, can be realized. Further, since the composition y of Mn is in the range of 0.5 <y <0.95, it is possible to achieve a high discharge voltage while maintaining a high capacity.

Also, the non-aqueous electrolyte cell 1, as the cathode active material, the general formula _{Li x Mn y Fe 1-y} PO 4 ( proviso that 0 <x ≦ 2, is 0.5 <y <0.95. a compound represented by), or the general formula _{Li x Mn y Fe z a 1-} (y + z) PO 4 ( proviso that 0 <x ≦ 2, a 0.5 <y <0.95, 0 .5 <y + z <1, and A is at least one metal element selected from Ti and Mg.). For this reason, this nonaqueous electrolyte battery 1 realizes a high discharge voltage in the vicinity of 4 V while maintaining a high capacity, and has excellent charge / discharge characteristics. Furthermore, since the capacity in the high voltage region near 4 V is improved, compatibility with current lithium batteries can be achieved.

  The nonaqueous electrolyte battery 1 according to the present embodiment as described above is not particularly limited in shape, such as a cylindrical shape, a square shape, a coin shape, and a button shape. The size can be

  In the above-described embodiment, the case where a nonaqueous electrolytic solution obtained by dissolving an electrolyte salt in a nonaqueous solvent is used as the nonaqueous electrolyte has been described as an example. However, the present invention is not limited thereto. Instead, the present invention can also be applied to the case where a solid electrolyte or a gelled solid electrolyte containing a swelling solvent is used as the nonaqueous electrolyte. The present invention can be applied to both a primary battery and a secondary battery.

Further, in the method of synthesizing the positive electrode active material, a mixture of powder of _{Li x Mn y Fe 1-y} PO 4 or _{Li x Mn y Fe z A 1-} (y + z) compound as a raw material for synthesizing PO ₄ heating However, the present invention is not limited to this, and the general formula Li _x Mn can be applied by applying various chemical synthesis methods other than solid phase reaction or solid phase reaction. can be synthesized _y Fe _1-y PO ₄ or _{Li x Mn y Fe z a 1-} (y + z) is represented by PO ₄ compound.

To examine the effect of the present invention were synthesized _{Li x Mn y Fe 1-y} PO 4. Then, a _{Li x Mn y Fe 1-y} PO 4 obtained by using as a positive electrode active material to prepare a battery, and its characteristics were evaluated.

Example 1
First, LiMn _0.6 Fe _0.4 PO ₄ was synthesized as a positive electrode active material.

In order to synthesize LiMn _0.6 Fe _0.4 PO ₄ , first, manganese carbonate (MnCO ₃ ), iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed so that the molar ratio is 1.2: 0.8: 2: 1, sufficiently pulverized and mixed by a ball mill, and then in a nitrogen atmosphere. A synthetic intermediate was prepared by performing preliminary firing at 300 ° C. for 3 hours. The obtained synthetic intermediate and acetylene black were mixed so that the weight ratio was 90:10, and further sufficiently pulverized and mixed by a ball mill, and then 450 ° C., 500 ° C., 600 ° C. or 700 in a nitrogen atmosphere. LiMn _0.6 Fe _0.4 PO ₄ was synthesized by heating at 24 ° C. for 24 hours.

Then, a battery was prepared using the LiMn _0.6 Fe _0.4 PO _4, obtained as described above as the positive electrode active material. Here, a battery was manufactured using LiMn _0.6 Fe _0.4 PO ₄ obtained by heating at 600 ° C.

First, 85% by weight of dried LiMn _0.6 Fe _0.4 PO ₄ as a positive electrode active material, 10% by weight of acetylene black as a conductive agent, 5% by weight of polyvinylidene fluoride as a binder, and N-methyl as a solvent. A paste-like positive electrode mixture was prepared by uniformly mixing in -2-pyrrolidone. As polyvinylidene fluoride, # 1300 manufactured by Aldrich was used.

  Next, this positive electrode mixture was applied onto an aluminum mesh serving as a current collector, and dried at 100 ° C. for 1 hour in a dry argon atmosphere to form a positive electrode active material layer.

  And the aluminum mesh in which the positive electrode active material layer was formed was punched in the disk shape of diameter 15mm, and it was set as the pellet-shaped positive electrode. One positive electrode carries 60 mg of active material.

  Next, a lithium metal foil was punched out in substantially the same shape as the positive electrode to obtain a negative electrode.

Next, a nonaqueous electrolytic solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol / l in an equal volume mixed solvent of propylene carbonate and dimethyl carbonate.

  The positive electrode obtained as described above was accommodated in a positive electrode can, the negative electrode was accommodated in a negative electrode can, and a separator was disposed between the positive electrode and the negative electrode. A non-aqueous electrolyte solution was injected into the positive electrode can and the negative electrode can, and the positive electrode can and the negative electrode can were caulked and fixed to prepare a 2025 type coin type test cell.

Comparative Example 1
First, LiMnPO ₄ was synthesized as a positive electrode active material.

In order to synthesize LiMnPO ₄ , first, manganese carbonate (MnCO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) have a molar ratio of 2: 2: 1. After being sufficiently ground and mixed by a ball mill, a synthetic intermediate was prepared by performing preliminary firing at 300 ° C. for 3 hours in a nitrogen atmosphere. The obtained synthetic intermediate was further sufficiently pulverized and mixed with a ball mill, and then heated at 600 ° C. for 24 hours in a nitrogen atmosphere to synthesize LiMnPO ₄ .

Next, a test cell was produced in the same manner as in Example 1 using the obtained LiMnPO ₄ as the positive electrode active material.

Next, a powder X-ray diffraction pattern was measured for LiMn _0.6 Fe _0.4 PO ₄ of Example 1 and LiMnPO ₄ of Comparative Example 1 synthesized by the method described above. The measurement conditions of powder X-ray diffraction are shown below.

Equipment used: Rigaku RINT2500 Rotating anti-cathode X-ray: CuKα, 40 kV, 100 mA goniometer: Vertical standard, radius 185 mm Counter monochromator: Used filter: Unused slit width: Divergent slit (DS) = 1 ° receiving slit (RS) = 1 ° Scattering slit (SS) = 0.15 mm Counting device: Scintillation counter Measurement method: reflection method, continuous scan scanning range: 2θ = 10 ° to 80 ° Scan speed: 4 ° / min. FIG. 2 shows powder X-ray diffraction patterns of LiMn _0.6 Fe _0.4 PO ₄ heated and synthesized at 500 ° C., 600 ° C. or 700 ° C., respectively. From Figure 2, the presence of impurities other than LiMn _0.6 Fe _0.4 PO ₄ was not confirmed in the product, it can be seen that LiMn _0.6 Fe _0.4 PO ₄ having an olivine structure of a single phase is obtained.

On the other hand, the powder X-ray diffraction pattern of LiMnPO ₄ synthesized in Comparative Example 1 is shown in FIG. FIG. 3 shows that single-phase LiMnPO ₄ is obtained.

  Moreover, the charge / discharge test was done about the test cell produced as mentioned above.

First, constant current charging was performed on each test cell, and when the battery voltage reached 4.5V, switching from constant current charging to constant voltage charging was performed while the voltage was maintained at 4.5V. . The charging was terminated when the current became 0.05 mA / cm ² or less. Thereafter, discharge was performed, and the discharge was terminated when the battery voltage dropped to 2.0V. Note that both charging and discharging were performed at room temperature (23 ° C.).

FIG. 4 shows the charge / discharge characteristics of a battery using LiMn _0.6 Fe _0.4 PO ₄ heated and synthesized at 600 ° C. in Example 1 as a positive electrode active material. FIG. 5 shows the charge / discharge characteristics of a battery using the synthesized LiMnPO ₄ as the positive electrode active material in Comparative Example 1.

As is apparent from FIG. 4, the battery using LiMn _0.6 Fe _0.4 PO ₄ as the positive electrode active material has a flat potential near 4 V in the first half of the discharge region and a flat potential near 3.4 V in the second half of the discharge region. And has a reversible charge / discharge capacity of about 146 mAh / g. On the other hand, as is apparent from FIG. 5, although LiMnPO ₄ having a single-phase olivine structure is used as the positive electrode active material, this battery does not have a flat discharge region and Mn redox does not occur. Recognize. From these results, it was found that LiMn _0.6 Fe _0.4 PO _{4 in} which a part of Mn was substituted with Fe realized Mn redox generation and could be used as a positive electrode active material having a high discharge voltage and a high capacity.

Then, to synthesize _{Li x Mn y Fe 1-y} PO 4 having an increased composition y of Mn. Then, a _{Li x Mn y Fe 1-y} PO 4 obtained by using as a positive electrode active material to prepare a battery, and its characteristics were evaluated.

Example 2
First, LiMn _0.7 Fe _0.3 PO ₄ was synthesized as a positive electrode active material.

To synthesize LiMn _0.7 Fe _0.3 PO ₄ , first, manganese carbonate (MnCO ₃ ), iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed so that the molar ratio is 1.4: 0.6: 2: 1, sufficiently pulverized and mixed by a ball mill, and then in a nitrogen atmosphere. A synthetic intermediate was prepared by performing preliminary firing at 300 ° C. for 3 hours. The obtained synthetic intermediate and acetylene black are mixed so that the weight ratio is 90:10, further sufficiently ground and mixed by a ball mill, and then heated at 600 ° C. for 24 hours in a nitrogen atmosphere. Thus, LiMn _0.7 Fe _0.3 PO ₄ was synthesized.

Next, using the obtained LiMn _0.7 Fe _0.3 PO ₄ as a positive electrode active material, a test cell was produced in the same manner as in Example 1.

Example 3
First, LiMn _0.75 Fe _0.25 PO ₄ was synthesized as a positive electrode active material.

In order to synthesize LiMn _0.75 Fe _0.25 PO ₄ , first, manganese carbonate (MnCO ₃ ), iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), and ammonium dihydrogen phosphate (NH ₄ H) ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed so that the molar ratio is 1.5: 0.5: 2: 1, sufficiently pulverized and mixed by a ball mill, and then in a nitrogen atmosphere. A synthetic intermediate was prepared by performing preliminary firing at 300 ° C. for 3 hours. The obtained synthetic intermediate and acetylene black are mixed so that the weight ratio is 90:10, further sufficiently ground and mixed by a ball mill, and then heated at 600 ° C. for 24 hours in a nitrogen atmosphere. Thus, LiMn _0.75 Fe _0.25 PO ₄ was synthesized.

Next, using the obtained LiMn _0.75 Fe _0.25 PO ₄ as a positive electrode active material, a test cell was produced in the same manner as in Example 1.

With respect to LiMn _0.7 Fe _0.3 PO _{4 of} Example 2 and LiMn _0.75 Fe _0.25 PO ₄ of Example 3 synthesized by the method as described above, powder X-ray diffraction patterns were measured under the same measurement conditions as in Example 1. . The powder X-ray diffraction patterns of LiMn _0.7 Fe _0.3 PO _{4 of} Example 2 and LiMn _0.75 Fe _0.25 PO ₄ of Example 3 are shown together in FIG.

Further, the produced test cell was subjected to a charge / discharge test in the same manner as in Example 1. FIG. 7 shows the charge / discharge characteristics of the battery using LiMn _0.7 Fe _0.3 PO ₄ of Example 2 as the positive electrode active material. Further, FIG. 8 shows charge / discharge characteristics of the battery using LiMn _0.75 Fe _0.25 PO ₄ of Example 3 as the positive electrode active material.

Further, a charge / discharge cycle test was performed on the battery using LiMn _0.7 Fe _0.3 PO ₄ of Example 2 as the positive electrode active material. The cycle characteristics of the battery of Example 2 are shown in FIG.

As can be seen from FIG. 6, LiMn _0.7 Fe _0.3 PO ₄ and LiMn _0.75 Fe _0.25 PO ₄ having a single-phase olivine structure are obtained.

As is clear from FIG. 7, the battery using this LiMn _0.7 Fe _0.3 PO ₄ as the positive electrode active material has a flat discharge region in the vicinity of 4 V, using the LiMn _0.6 Fe _0.4 PO ₄ shown in FIG. And a reversible charge / discharge capacity of about 146 mAh / g is generated. Further, as apparent from FIG. 8, the battery using this LiMn _0.75 Fe _0.25 PO ₄ as the positive electrode active material has a flat discharge region in the vicinity of 4 V, and LiMn _0.7 Fe _0.3 PO ₄ shown in FIG. As a result, the battery has a reversible charge / discharge capacity of about 146 mAh / g. For these reasons, in _{Li x Mn y Fe 1-y} PO 4, as taking a value composition y is large Mn, that is, as relatively increasing the composition of Mn relative to Fe, it can realize a high discharge voltage I understood. Moreover, it has been found that even if the composition y of Mn is increased, the capacity is not reduced.

Further, as is apparent from FIG. 9, the battery using LiMn _0.7 Fe _0.3 PO ₄ of Example 3 as the positive electrode active material maintains a discharge capacity of about 146 mAh / g even when charging and discharging are repeated. It was found to have good cycle characteristics.

Then, Li part of _{x Mn y Fe 1-y PO} 4 in Mn and Fe, which is a compound obtained by substituting in combination with Fe, and at least one metal element A selected from Ti or Mg, Li It was synthesized _{x Mn y Fe z a 1- (} y + z) PO 4. Then, a _{Li x Mn y Fe z A 1-} (y + z) PO 4 obtained by using as a positive electrode active material to prepare a battery, and its characteristics were evaluated.

Example 4
First, LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ was synthesized as a positive electrode active material.

In order to synthesize LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ , first, manganese carbonate (MnCO ₃ ), iron oxalate (FeC ₂ O ₄ .2H ₂ O), titanium oxide (TiO ₂ ), and ammonium dihydrogen phosphate ( NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed so that the molar ratio is 1.4: 0.4: 0.2: 2: 1, and sufficiently pulverized by a ball mill. After mixing, a synthetic intermediate was prepared by performing preliminary firing at 300 ° C. for 3 hours in a nitrogen atmosphere. The obtained synthetic intermediate was further sufficiently pulverized and mixed by a ball mill, and then heated at 600 ° C. for 24 hours in a nitrogen atmosphere to synthesize LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ .

Next, using the obtained LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ as a positive electrode active material, a test cell was produced in the same manner as in Example 1.

For the LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ of Example 4 synthesized by the method as described above, the powder X-ray diffraction pattern was measured under the same measurement conditions as in Example 1. FIG. 10 shows a powder X-ray diffraction pattern of LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ . Further, the produced test cell was subjected to a charge / discharge test in the same manner as in Example 1. FIG. 11 shows the charge / discharge characteristics of the battery using LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ as the positive electrode active material.

As can be seen from FIG. 10, LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ having a single-phase olivine structure is obtained. As is clear from FIG. 11, the battery using this LiMn _0.7 Fe _0.2 Ti _0.1 PO ₄ as the positive electrode active material has a flat potential in the vicinity of 4V. From these facts, it was found that LiMn _0.7 Fe _0.2 Ti _0.1 PO _{4 in} which a part of Mn and Fe was substituted with Ti realized redox generation of Mn and could be used as a positive electrode active material having a high discharge voltage.

  It was also found that a high discharge capacity of 155 mAh / g can be obtained by substituting Mn with Fe and Ti in combination.

Example 5 First, LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ was synthesized as a positive electrode active material.

In order to synthesize LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ , first, manganese carbonate (MnCO ₃ ), iron oxalate (FeC ₂ O ₄ .2H ₂ O), and magnesium oxalate (MgC ₂ O ₄ .2H ₂ O) And ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed so that the molar ratio is 1.4: 0.5: 0.1: 2: 1. After sufficiently pulverizing and mixing with a ball mill, a synthetic intermediate was prepared by performing preliminary firing at 300 ° C. for 3 hours in a nitrogen atmosphere. The obtained synthetic intermediate was further sufficiently pulverized and mixed by a ball mill, and then heated at 600 ° C. for 24 hours in a nitrogen atmosphere to synthesize LiMn _0.7 Fe _0.25 Mg _0.05 PO 4.

Next, using the obtained LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ as a positive electrode active material, a test cell was produced in the same manner as in Example 1.

For the LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ of Example 5 synthesized by the method as described above, a powder X-ray diffraction pattern was measured under the same measurement conditions as in Example 1. FIG. 12 shows a powder X-ray diffraction pattern of LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ . Further, the produced test cell was subjected to a charge / discharge test in the same manner as in Example 1. FIG. 13 shows charge / discharge characteristics of a battery using LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ as a positive electrode active material.

As can be seen from FIG. 12, LiMn _0.7 Fe _0.25 Mg _0.05 PO 4 having a single-phase olivine structure is obtained. As apparent from FIG. 13, the battery using this LiMn _0.7 Fe _0.25 Mg _0.05 PO ₄ as the positive electrode active material has a flat potential in the vicinity of 4V. From these results, it was found that LiMn _0.7 Fe _0.25 Mg _0.05 PO _{4 in} which a part of Mn and Fe was replaced with Mg realized redox generation of Mn and could be used as a positive electrode active material having a high discharge voltage.

  Moreover, it turned out that a high discharge capacity can be obtained by substituting Mn with Fe and Mg in combination with Example 2 in which Mn is substituted with Mg alone.

1 Nonaqueous electrolyte battery, 2 negative electrode, 3 negative electrode can, 4 positive electrode, 5 positive electrode can, 6 separator, 7 insulating gasket

Claims (3)

Formula _{Li x Mn y Fe 1-y} PO 4 ( where 0 <x ≦ 2, 0.5 <y <0.95.) The method of producing a cathode active material containing a compound represented by Because
A mixing step in which a plurality of substances that are the raw materials for the synthesis of the compound are mixed to form a precursor;
A firing step of firing and reacting the precursor obtained in the mixing step,
The plurality of substances include iron oxalate,
The firing temperature of the precursor in the firing step is in the range of 350 ° C. or more and 790 ° C. or less,
In the above mixing step, a reducing agent is added and mixed to form a precursor,
The reducing agent is iron powder ,
The said iron powder is a manufacturing method of the positive electrode active material added to the said precursor in 1 to 30 weight% with respect to the sum total of Fe in the iron raw material of the said synthetic raw materials .   The method for producing a positive electrode active material according to claim 1, wherein the firing temperature of the precursor in the firing step is in the range of 450 ° C. or higher and 700 ° C. or lower. The method for producing a positive electrode active material according to any one of claims 1-2 to perform the baking of the precursor in an inert gas atmosphere.

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